The present invention relates to a method of and an installation for hot dip coating of metal strips, in particular, of a hot rolled steel strip, in which the metal strip is transformed into a continuous strip in an unwinding station with an adjoining welding machine, and then the continuous strip is subjected to a downstream modifying process including primary and secondary prickling and, in the final treatment step, in the hot dip coating section, guiding the continuous strip through a melt bath.
For hot dip coating of a hot strip but also of an as-rolled and/or cold annealed strip, it is known to transform a strip coil into a continuous strip or make available a continuous strip by welding respective coil ends with beginnings of the following coils in an unwinding station that includes, e.g., a twin or turret reel and an adjoining the reel, welding machine. The unwinding station is adjoined by a looping accumulator in vertical or horizontal implementation which insures effecting a following continuous treatment process. The oxidized strip, which provides for a non-insignificant portion of dust, is stored in the looping accumulator. Therefore, the accumulator should be encapsulated. After leaving the looping accumulator, the strip, in the first operational step, is pulled through a stretcher-and-roller leveller to achieve a desired flatness of the strip. During this process, breaking and partial flaking-off of the scale layer take place. This requires that the fallen-off particles be aspirated and filtered. In addition, the roller supports of the stretcher-and-roller leveller should be protected against the finest scale particles which is very expensive and, to this end, the stretcher-and-roller leveller is entirely encapsulated.
The strip, which runs out of the stretcher-and-roller leveller, in known plants, is transported in a pickling station in which the scale layer and reaction products are removed from the strip surface. In a further operational step, the strip runs through an adjoining rinsing station in order to rinse off the residues of pickling products from the strip surface before the strip is introduced into the drying station to be dried there. A secondary pickling installation with a following rinsing installation can adjoin the primary pickling installation with its rinsing installation and be arranged in front of the drying installation. Finally, from the drying station, in a following operational step, the strip is introduced into a furnace with a protective gas atmosphere where the strip is brought to a coating temperature before it, in the last operational strip, is guided through a melt bath to provide the surface of the strip with a metallic coating.
The object of the invention is to provide a method and an installation of the type described above which would permit to conduct a variable coating process with reduced costs.
According to the invention, this object is achieved by a method that includes transporting a continuous strip, in a first treatment step, directly into a pickling installation. An installation for effecting the process contemplates, according to the invention, providing the primary pickling installation in the entry section which is separated from hot dip coating section by an entry accumulator.
Because the metal strip, according to the invention, after leaving the welding machine, runs in directly into the pickling installation, numerous advantages are simultaneously obtained. Thus, it is insured that in the following sections of the installation, the rinsing station and the drying station, which follow the pickling installation, a scale-free metal strip is treated, which makes encapsulation of the entry accumulator and of the stretcher-and-roller leveller unnecessary. The stretcher-and-roller leveller can be simply formed because an extensive scale suction is eliminated. Furthermore, separation or decoupling of the primary pickling installation from the hot dip coating process is achieved. Thus, advantageously, the first entry accumulator is arranged between the welding machine and the immediately following it, the primary pickling installation, and the second strip accumulator is arranged in front of the hot dip coating section and behind the primary pickling installation. A short stoppage in the pickling station does not require, as in the conventional processes, stoppage of the hot dip coating process, which results in production of scrap. And vice versa, a short stoppage of the hot dip coating process does not result in overpickling of the strip in the primary pickling installation because the following it, looping accumulator has an adequate receiving capacity. In addition, the adjoining the pickling installation, accumulator is kept scale-free.
For a combined operation with a hot strip and a cold strip in an as-ready or annealed condition, the advantage consists in that upon conversion to an operation with a cold strip, no preliminary rinsing of the accumulator, rolls, and the stretcher-and-roller leveller is necessary. Thereby, the waste time is minimized, and the quality of the strip is improved.
In the installation, the entry section of which advantageously includes a primary pickling installation, a rinsing station, and following it, drier, and the hot dip coating section of which includes following each other, stretcher leveller, secondary pickling installation, rinsing installation, drier, and a furnace located upstream of the melt bath, the secondary pickling installation, which has small dimensions, serves for activating of the steel strip surface, which insures the quality of the subsequent coating.